Duplication of Two Acetaminophen Products in a 20-Month-Old
Ms. L. brings her 20-month-old son, weight 10.4 kg, to your pharmacy counter at 09:00. He has had a fever up to 38.9 °C for 2 days with rhinitis and is drinking well. She has been giving 'Infants' Tylenol' (80 mg/0.8 mL) 1.2 mL every 4 hours, and because he remained febrile overnight she also gave 'Children's Tylenol' (160 mg/5 mL) 5 mL at 22:00, 02:00 and 06:00. Her dosing log shows infant-product doses at 08:00, 12:00, 15:00 and 18:00, then the three children's-product doses. He is now playful and afebrile, with no vomiting, abdominal pain or lethargy. She asks whether she can give another dose now and whether she should 'switch to the stronger one' because the infant drops 'don't seem to work.' She has not used any cold or cough products.
1. Calculate the acetaminophen dose the child received and determine whether this represents a toxic ingestion. Show your work.
Read the worked answer
Convert both products to mg and to mg/kg (weight 10.4 kg).
| Product | Concentration | Dose given | mg per dose | Number | Total |
|---|---|---|---|---|---|
| Infants' Tylenol 80 mg/0.8 mL | 100 mg/mL | 1.2 mL | 120 mg | 4 | 480 mg |
| Children's Tylenol 160 mg/5 mL | 32 mg/mL | 5 mL | 160 mg | 3 | 480 mg |
Total = 960 mg over about 22 hours (08:00 to 06:00 next day).
- Per kg: 960 ÷ 10.4 = 92 mg/kg in roughly one day.
- Recommended maximum: 15 mg/kg/dose, no more than 75 mg/kg/day (and no more than 5 doses/24 h). 75 × 10.4 = 780 mg/day. She gave about 23% above that.
- Largest single dose: 160 mg = 15.4 mg/kg, which is at, not above, the per-dose limit.
Interpretation: this is a repeated supratherapeutic exposure, not an acute toxic ingestion. The referral threshold for a single acute ingestion is about 150 mg/kg (four-hour level), and the child is nowhere near that. Repeated doses above 75–100 mg/kg/day for more than 48 hours, or any symptoms (vomiting, abdominal pain, lethargy, jaundice), would warrant poison-centre consultation and liver enzymes/INR. Here: one day, no symptoms, so the risk of hepatotoxicity is low, but the mother must stop the current pattern.
2. What advice do you give the mother now, including how to dose each product and when to seek care?
Read the worked answer
Now: no further dose at 09:00; the last dose was 06:00, so the next is due around 10:00–12:00.
Correct dosing (choose one product only):
- Infants' drops (100 mg/mL): 15 mg/kg = 156 mg → 1.5 mL (150 mg) every 4–6 h, maximum 5 doses/24 h (750 mg).
- Children's suspension (32 mg/mL): 15 mg/kg = 156 mg → 5 mL (160 mg) every 4–6 h, maximum 4 doses/24 h (640 mg) to stay under 75 mg/kg/day.
Give the dosing device that comes with the product; do not use a kitchen spoon. Write the times down.
Explain the 'stronger' misconception: the infant drops are more concentrated (100 mg/mL vs 32 mg/mL), so 1.2 mL of drops is not the same as 1.2 mL of suspension. That is exactly how the double-dosing happened.
Fever care: fluids, light clothing, antipyretic for comfort rather than to normalize the number. Ibuprofen 10 mg/kg (≈100 mg) q6–8h can be used if she prefers, but do not alternate regimens unless she can track them; avoid combination cold products that contain acetaminophen.
Seek care now if: repeated vomiting, abdominal pain, lethargy, jaundice, rash, dehydration, or fever beyond 3 days. Otherwise follow up with her physician if fever persists.
3. How would your assessment change if the mother reported 4 days of this pattern, or if the child weighed 8 kg?
Read the worked answer
Four days of this pattern: cumulative exposure would be roughly 3,800 mg (≈365 mg/kg) over 4 days, well into the repeated supratherapeutic range. That changes the plan: stop all acetaminophen, contact the provincial poison centre, and arrange same-day AST/ALT, INR and a clinical assessment, even if asymptomatic. Symptoms can lag 24–72 hours.
If the child weighed 8 kg: 960 mg ÷ 8 = 120 mg/kg/day (60% above the 75 mg/kg/day maximum), and each 160 mg suspension dose would be 20 mg/kg - above the 15 mg/kg per-dose limit. That is a higher-risk exposure and would push me toward poison-centre contact and bloodwork rather than observation alone.
General principle: the mg/kg calculation, not the number of doses or the product name, drives the decision. Document the calculation, the advice given and the rationale, and record that the mother was told which product to use and how to measure it.